Method of and drive for actuating absorber rods in pebble bed reactors

Abstract

A method of actuating absorber rods in pebble bed reactors, according to which the rod is moved into or out of the ball pile with limited advancing speed in a turning or rotary manner. A feeding or advancing force is transmitted onto the rod being introduced, and this force does not exceed the appropriate maximum value of the ball strength and the rod stability. The drive provided for the foregoing procedure effects both a longitudinal shifting and rotation of a rod connected therewith, and has an axially fixed advancing spindle, the spindle nut of which is rigidly connected with the absorber rod and is journalled in a rotary pipe or tube in such a way as to be axially displaceable yet fixed against rotation, with the rotary tube being driven at a constant speed. During removal or outward travel of the rod from the ball pile, a fixed transmission ratio exists between the driving mechanism and driven end, which fixed transmission is generated with the aid of a freewheel or free-running drive. A coupling is provided between the drive motor and the spindle to limit the transferrable torque or turning moments according to a predetermined characterizing line or curve, whereby the rotary speed of the spindle is limited during introduction of the rod into the ball pile by the freewheel or free-running drive causing engagement when the driven end speed of the coupling equals the driving speed. The coupling between the drive motor and the spindle may be found by a hydraulic coupling of oil pump and oil motor, or by a Fottinger coupling.

What I claim is: 
     
       1. A drive for actuating absorber rods in pebble bed reactors, with which a respective rod is selectively movable into and out of the ball pile in a rotary manner with limited advancing speed and with both a longitudinal displacement as well as a rotation of a rod operatively connected therewith, said drive comprising in combination; a drive motor;   an axially fixed advancing spindle having a spindle nut rigidly connected with said absorber rod;   a rotary tube driven at constant speed, said spindle nut being journalled in said rotary tube in such a way permitting said nut to be axially displaceable yet having said nut fixed against rotation in said tube;   a free-running drive or freewheel operatively connected with said drive motor and said spindle, removal of said rod from said ball pile occurring at a fixed ratio between driving mechanism and driven end by said freewheel; and   a hydrodynamic torque limiting coupling provided between said drive motor and said spindle to limit transferrable torque, the rotary speed of said spindle being limited during introduction of said rod into said ball pile by said free-running drive causing engagement when the driven end speed of said coupling equals the driving speed by transmitting to said rod an advancing force commensurate with ball strength and rod stability so that ball destruction and bending-through of the rod are safely avoided wherein the linear movement of said rod is transmitted thereto only by said coupling.   
     
     
       2. A drive in combination according to claim 1, in which said coupling comprises a hydraulic coupling of an oil pump and an oil motor. 
     
     
       3. A drive in combination according to claim 1, in which said coupling comprises a fluid torque converter. 
     
     
       4. A method of actuating absorber rods in pebble bed reactors according to claim 1, according to which a respective rod is selectively moved into and out of the ball-pile in a rotary manner with limited advancing speed, said method comprising in combination therewith the step of transmitting to said rod through a fluid coupling only an advancing force commensurate with the ball strength and the rod stability so that ball destruction and bending-through of the rod are safely avoided.